In an inverter and a voltage converter configured to drive a motor for running an electric automobile, there is a case where a semiconductor device (a semiconductor package) having a semiconductor element handling a large amount of current molded with plastic, is used (refer to Japanese Patent Application Publication No. 2006-179655). A typical example of such a semiconductor element is a transistor used in a switching circuit. Hereinafter, a block of plastic which molds a semiconductor element will be also referred to as a “plastic mold”. The plastic mold is formed by an injection molding. Metal plates called lead frames are respectively attached to both sides of the plastic mold. The semiconductor element inside the plastic mold is bonded to each of the lead frames. The lead frame is sometimes used as an electrode, and is also used as a mere heat sink. A solder material is typically used for bonding between the lead frame and the semiconductor element. However, materials other than the solder material, such as nickel nanoparticles for example may be used for the bonding. Hereinafter, a material for bonding the lead frame and the semiconductor element will be called a “bonding material”.
A semiconductor element is molded with plastic for purposes of protecting the semiconductor element from external dusts and moisture, and suppressing fatigue degradation of a bonding material that bonds the semiconductor element and the lead frame. Because the semiconductor element and the lead frame have different coefficients of thermal expansion, stress is repeatedly applied to the bonding material in a heat cycle generated by the semiconductor element. Deformation of the semiconductor element and the lead frame can be suppressed by molding a part of the lead frame and the semiconductor element with the plastic. As a result, the stress applied to the bonding material is suppressed, and accordingly the fatigue degradation of the bonding material is suppressed.